An object placed in a moving fluid experiences a net force when the speed of the fluid is greater on one side of the object than on the other. This is due to a difference in pressure on the two sides of the object and is known as the Bernoulli effect. A number of demonstrations of this Bernoulli effect have appeared in the physics teaching literature.1–4 In this article, we describe two such demonstrations that are quite dramatic and suitable for showing to large classes.5

Phase changes in waves are just varied enough and just unfamiliar enough to students to be confusing. The phase changes upon reflection of waves on a string and of sound waves are usually the first to be encountered by students, and can give a bridge to other such changes found, for example, in electromagnetic waves. Before digital oscilloscopes,phase changes in sound waves had to be taken on faith or tested indirectly. Now they are quite easy to show. This note describes an experiment that demonstrates phase changes of a reflected sound pulse in a long air-filled tube. The demonstration also gives an easy and straightforward measurement of the speed of sound, and shows that air temperature matters while pressure does not, as theory predicts.1

In this paper we propose some very useful and interesting experiments that are quite simple and can be done by teachers or students. The equipment used for these experiments is not expensive; the major device of each experiment is the voltage tester (sometimes called a “neon screwdriver”).1

Logarithmic intensity scales are widely encountered in astronomy (star magnitudes), acoustics (decibels),seismology (the Richter scale), and elsewhere. Yet students often have difficulty mastering the concept of logarithmic scales. With this note, I am calling attention to a case of the application of a logarithmic scale to something that is simple, transparent, and widely understood. The simplicity of the example is such that it will allow the merits and use of logarithmic scales to be more easily grasped by students. The understanding of this simple logarithmic scale can then be applied to the comparison of sound intensities.

The astronomy curriculum at Las Positas College is a familiar one to many readers — a lecture course on the solar system, another on stars and galaxies, and a separate laboratory course. The laboratory therefore has students who have never heard of some topics, and others who have just had lectures on them. Also, many topics cannot be brought into the laboratory, leading us to rely heavily upon computer-based exercises. Two of these are Kepler's laws of planetary motion and stellar structure. In developing these exercises, we have explored the use of the Microsoft® Excel spreadsheet program. Excel has the advantage of being easier to learn and implement than Java, while also being able to do sophisticated computations.1, 2 At the same time, it may be used to present material in a visually appealing manner, resembling the layout of webpages.

Devices familiar to students are always good examples to illustrate physics concepts. I have found the right-side mirrors of cars to be one of these illustrative devices, especially because of the mysterious label printed on them: Warning! Objects in mirror are closer than they appear. Finding the physical reason for the label is a very interesting exercise that may be used to review or introduce some optical concepts.

The now widespread use of microcomputers in introductory physics laboratories allows for an addendum to the traditional mass-spring-system experiment that usually culminates with the determination of the spring constant k. A sonic-motion detector can be used to create plots of position, velocity, and acceleration as functions of time and even position versus velocity. Students can then be asked to compare these plots and observe the relationships between the variables. This, however, is only the beginning. The use of features of the data-collection software allows for further and even more informative analysis.

In this paper, we offer three examples, inspired by Galileo's work, for connecting the physics of the pendulum with free fall and the inclined plane. The first example discusses the time it takes for a ball to slide down a frictionless inclined plane along a chord, drawn from the lowest point of a vertical circle to any point on the circle. The second example discusses a timing method that Galileo tested in measuring free fall directly, and the third example outlines an approach we have developed for accurately calculating the period of a pendulum for any angle, using only the kinematics of acceleratedmotion along an inclined plane, first studied by Galileo.

One of the key subjects in introductory physics is the problem of collisions. It provides a nice example where conservation laws of energy and momentum are essential. Two extreme cases are usually solved: elastic and perfectly inelastic collisions. In the very simple one-dimensional case, velocities before and after collision are readily related through the masses of the colliding bodies. Similar solutions can be found for partially inelastic collisions, provided that the degree of energy loss is known. Otherwise, the energy balance equation cannot be written down. Usually, one can reasonably assess whether the collision is perfectly inelastic (for instance, a bullet impinging onto a piece of wood). However, it is a matter of faith to consider a priori a collision as elastic or as being in any intermediate situation. We hope this statement will become clearer to the reader by the end of this paper.

The fact that, despite 12 years of education, even our top college students have partially or completely mistaken ideas about science in general, and physical science in particular, is disturbing but to a certain extent expected. Students have received all sorts of scientific, pseudoscientific, and non-scientific information through their daily experiences, their own environment explorations, their social interactions, media, and formal instruction. As a consequence of their constant constructing, deconstructing, processing, and organizing the received information, college students will have ideas that are not currently supported by the scientific community.

When measuring potential difference or current with an analog meter employing a moving-coil galvanometer, the user has to be sensitive to circuit changes produced by the internal resistance of the meter. Fortunately, analog meters have been largely replaced with digital instruments that ordinarily have negligible effect on the measurements. Nevertheless, there are situations where a digital meter can seriously affect the circuit. We report here such a situation that was embarrassing initially but proved to be instructional in the end.

The longitudinal1normal modes of vibration of rods are similar to the modes seen in pipes open at both ends. A maximum of particle displacement exists at both ends and an integral number (n) of half wavelengths fit into the rod length. The frequencies of the normal modes is given by Eq. (1), where L is the rod length and V is the wavevelocity: Many methods have been used to measure the velocity of these waves. The Kundt's tube method commonly used in student labs will not be discussed here. A simpler related method has been described by Nicklin.2 Kluk3measuredvelocities in a wide range of materials using a frequency counter and microphone to study sounds produced by impacts. Several earlier methods4,5 used phonograph cartridges complete with needles to detect vibrations in excited rods. A recent interesting experiment6 used wave-induced changes in magnetization produced in an iron rod by striking one end. The travel time, measured as the impulsive wave reflects back and forth, gave the wavevelocity for the iron rod. In the method described here, a small magnet is attached to the rod with epoxy, and vibrations are detected using the current induced in a few loops of wire. The experiment is simple and yields very accurate velocity values.

One common paradox students find perplexing in learning about electric current is the apparent contradiction between the tiny drift speed of free electrons in a conductor, say about 1 m/h, and the response of a current “in no time” when the circuit is switched on or off. These phenomena can be understood in terms of the speed of the electrical signal, which travels at or near the speed of light. As soon as the circuit is closed, apart from inductive delay, an electric field is set up almost simultaneously throughout the circuit. It is the electric field that causes electrons to start drifting at all points in the circuit. This paper describes an experiment for measuring the speed of an electromagnetic signal in a coaxial cable.

The PASCO Coulomb's law apparatus has a very sensitive torsion balance on which a sphere capable of holding a static charge is suspended. Rapid motion in the vicinity of the balance, breathing directly on the sphere, or air currents from ventilation will all move the sphere around significantly. This motion makes it very difficult to obtain meaningful data. In fact, the sphere moves so much under the influence of the ventilation in our lab that it was not possible to obtain repetitive results.